Fracture conductivity - Design considerations and benefits in unconventional reservoirs

Hydraulic fracturing is critical to the success of the petroleum industry in the twenty-first century, turning previously uneconomic reservoirs into success stories through the application of horizontal wellbores and multiple transverse fracture treatments. The ability to contact large volumes of rock in these ultra-tight reservoirs through a single horizontal wellbore has allowed for reduced cost of drilling when compared to multiple vertical wells. While most engineers tend to understand the wellbore and its components, the hydraulic fracture treatment is typically less understood. However, the wellbore and the hydraulic fractures are expected to provide a conductive flow path to the reservoir for the life of the well, so the comprehension of each are critical to the long term viability of the completion. Of course when it comes to the hydraulic fracture, the proppant is the material that is expected to provide this long term connectivity (a.k.a. conductivity), so its selection should be treated the same as the selection of wellbore components - it should be chosen by looking at all phases of the well's production, including the service when the well is first placed on production, the environment if/when the well is placed on artificial lift, and the conditions when the well is producing 20 years later. This paper will present a thorough review of fracture conductivity principles, with particular emphasis on the impact that downhole conditions has on its realistic measure. After reviewing the primary parameters that will impact fracture conductivity, the authors will review the main components of proppant selection, specifically as it relates to the process in unconventional reservoirs over the last several years, and will present a methodology which will lead a design engineer to the optimal fracture design. Finally, case histories which illustrate the application of these theories will be presented for actual completions in both the Bakken and Eagle Ford plays. This paper will be beneficial to those engineers and technologists who are interested in designing optimal completions in their wells and maximizing the return on their investment. (C) 2014 Elsevier B.V. All rights reserved.